1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile.
2. Description of the Related Art
Conventionally, an electrophotographic image forming apparatus typified by Carlson's process is known. This image forming apparatus evenly charges a photosensitive element with a photoconductive characteristic to form a latent image as a charge distribution by image exposure corresponding to an image pattern. Subsequently, the image forming apparatus visualizes an image using colored resin microparticles (hereinafter referred to as toner) that are charged positively or negatively. Subsequently, an electrostatic force allows the toner to be transferred and moved onto a surface of a transferring material typified by a decalcomania paper. The transferring material passes through between pressed rollers. This allows obtaining a final toner image by fixing the toner on the transferring material using elasticity of the toner.
Japanese Patent Application Laid-open No. and Japanese Patent Application Laid-open No. 2003-84497 disclose image forming apparatuses that employ low temperature fixing using toner with a low peak temperature of loss elastic modulus.
Nowadays, a full-color image forming apparatus becomes mainstream using toners of four colors of black (hereinafter referred to as K), cyan (hereinafter referred to as C), magenta (hereinafter referred to as M), and yellow (hereinafter referred to as Y). Material applicable to toner of each color has been examined.
The full-color image forming apparatus is preferred to employ toners of the respective colors that each have approximately the same value of the peak temperature of loss elastic modulus. The loss elastic modulus is a measure of energy quantity where a stress applied to a toner is dissipated as heat at a deformation. The reason why the toners of the respective colors each have approximately the same value of the peak temperature of loss elastic modulus are used is as follows. This allows fixing the respective colors at the same fixing temperature and easily determining fixing temperatures. However, even if a toner that has a low peak temperature of loss elastic modulus and is easily softened and melted is developed, a toner of a certain color may be manufactured while a toner of another color might not be manufactured as follows. For example, matching of colorant (pigment and dye) causes a problem in a toner manufacturing process. As a result, manufacturing all the toners of four colors of K, C, M, and Y as toners with low values of peak temperature of loss elastic modulus has been difficult.
However, radiant heat of a fixing device and heat of a driving motor that drives, for example, a photosensitive element increases a temperature of a specific developing device that houses the toner with a low peak temperature of loss elastic modulus. In this specific developing device, the toner with a low peak temperature of loss elastic modulus is softened and condenses into a lump, which is blocking. The occurrence of blocking has been a problem.
The present invention has been made in view of the above-described circumstances, and it is an object of the present invention to provide an image forming apparatus that prevents blocking from occurring inside of a housing unit where a toner with a low peak temperature of loss elastic modulus is housed.